Give us some information and we can help you out.
You'll need to know:

1) The motherboard being used
2) The FSB being used on the processor
3) The rated clock speed, voltage and core of the processor
4) The speed of RAM being used
5) The average temperature of the processor currently
6) What type of cooling is being used / is available

Read the sticki'ed topics in the Cooling and Modding forum and this one, especially this thread:

1) The motherboard being used ASUS
2) The FSB being used on the processor 145MHZ
3) The rated clock speed, voltage and core of the processor
4) The speed of RAM being used
5) The average temperature of the processor currently 37*C
6) What type of cooling is being used / is available ANTEC FAN AND HEATSINK

145mhz FSB would already be an overclocked processor, or at least an overclocked FSB. Standard FSB for Duron and Athlon Thunderbird is 100mhz or 133mhz. If it is really at 145 someone has already overclocked the system.

Overclocking is the process of manipulating the CPU and other components of your computer to run faster than the manufacturers rated speed. Why would you want to overclock your computer? Overclocking can improve performance in tasks such as resource-intensive games, programs running large databases, extensive graphics editing, and video rendering. The budget conscious could also save money on their processor by purchasing a cheaper low-end CPU that can be overclocked to higher specs. And there's always the bragging rights of having that really fast, super-tweaked system.

How Speed is Measured
With computer components, speed is measured as a unit of frequency called hertz (Hz); one hertz is one cycle per second. For example, common house current in the United States cycles at 60 Hz and in Europe it cycles at 50 Hz. In today's computers CPU speed is expressed in megahertz (millions of cycles per second) or gigahertz (billions of cycles per second). CPU instructions require a certain number of cycles to complete their task. Therefore, more cycles per second means more tasks can be accomplished in that second.

Why We Can Overclock
CPUs that are rated for different speeds are manufactured using the same process and at the same time. When chips are made, in particular processors, they are sorted based on tests done during the manufacturing process. If a chip is tested at the highest speed level and fails, it will be tested at successively lower levels until it passes. The chips are then sorted into bins according to the speeds they were tested at and passed. This is called speed binning. This also allows chip makers to produce one core chip for a particular model and then use speed binning to be able to offer a complete product line from low-end to high-end.

Early in the manufacturing process for a new CPU, manufacturers have a harder time getting chips to pass the high-end tests. The technology is newer, the process is newer, and the manufacturing techniques aren't fully tweaked yet. At this stage, there are more chips that don't pass the high-end tests and end up being binned as low-end chips. When a new CPU hits the market and the manufacturing process for that chip is young, you will have less chance getting a CPU that can be overclocked. At this stage, testing is more rigorous and binning is more exact. If it's binned at 2.4 GHz, for example, you probably won't be able to overclock it much beyond that, if at all.

Chip makers are constantly trying to improve and tweak their manufacturing processes. As the process matures and improves, more chips will pass at the higher levels and there will be more high-end chips than there are low-end chips. Some of these faster chips will be labeled and sold at lower rated speeds even though they passed the higher grade testing and can run at the faster speeds. Here's why...

Now that the manufacturing process has matured, many (if not most) chips will pass the speed tests at the high-end. The high-end speed bins will fill up faster than the low-end bins. Suppose the market demand is calling for more of the low-end CPUs for a particular model but the manufacturer now has more chips passing the higher speed binning tests. They will likely run short of the slower processors to meet market demand. And they can only sell so many of the top rated CPUs. That's the nature of the market. In order to fulfill market demand, they take high-end CPUs, label and sell them at the low-end speed and price. The reasoning is that it's better to make a little money on a lot of chips than no money on chips that aren't selling.

What does this mean for you? It means that when the manufacturing process has matured for a particular chip, you have a better chance of getting a high-end CPU that is labeled as low-end. It also means it may be easier to overclock this low-end CPU because there's a better chance that it's faster than labeled.

You won't know how much you can overclock any particular chip until you try. There is no way to tell exactly how much an individual CPU can be overclocked, but buying a lower-end CPU from a more mature manufacturing process will give you the best odds. It's always going to be easier to overclock a low-end chip rather than a high-end chip and even more so with a CPU from a mature manufacturing process.

How to Overclock
There is no one-guide-fits-all for overclocking. Each computer is different and each needs to be treated differently. Even identical components will act differently when overclocked. You need to learn about your particular system and each of its individual components. A good place to start is the TechSPot forums.

Your motherboard manufacturer's website is another place you should visit. Some possible needs are updates for your BIOS, a backup utility for your BIOS, the latest chipset drivers for your motherboard, and the most up-to-date manual for your motherboard.

Chip manufacturers don't support overclocking so it will most likely void your warranty. Mistakes could cause damage to components; you need to know your particular computer hardware and how to overclock that hardware. You will shorten the lifespan of your components by as much as 35% according to some estimates. Keeping the components properly cooled will help lessen the impact of this. Though overclockers say that this shortened lifespan isn't an issue with them since the functional lifespan of a computer is approximately 10 years and most of us will upgrade long before that.

Keeping your components cooled, preferably to temperatures even lower than the suggested temps, is necessary for overclocking. This may involve water-cooling, phase-change cooling, or heat pipes for air-cooling.

Components for Overclocking
A custom built computer is the way to go for overclockers. Dell, Gateway, etc. while decent computers in their own right, probably won't cut it for overclocking. The settings that you need to access in order to overclock are either hidden or not accessible on name brand computers. You need a motherboard that will let you change the various settings required for overclocking.

As you research you'll see motherboard brand names such as EPoX, Asus, DFI, Abit, and MSI mentioned frequently. These are great boards for the overclocker. Both Intel and AMD processors can be overclocked. There are avid fans of both and you won't have any trouble finding opinions about each.

Memory brands like Corsair, Kingston, and OCZ all have their supporters but one thing remains constant when it comes time to choose which memory you will use for overclocking - choose quality memory that is right for your particular system.

Good quality power is needed for any system and it becomes even more critical in an overclocked computer. It doesn't take much voltage fluctuation to result in an unstable system. A cheap power supply is just asking for trouble. Quality brands like Antec or Enermax are a must for the serious overclocker.

If you choose to overclock your video, brands such as PNY, Sapphire, and MSI are mentioned frequently as the top choices by overclockers. Video is overclocked by using software programs such as Powerstrip or Rivatuner and you can find links for these and other such programs in the TechSPot forums too. You may also need to investigate upgrading the BIOS of your video card. It can't be said enough, but research and learning before doing is the key to overclocking and video is no exception to this rule.

Benchmarking and testing for stability as you make incremental changes in your overclocking process is a must-do. Links for programs like Prime95, 3DMark, SiSoft Sandra, Memtest86, and others can also be found in our forums.

Overclocking isn't for everyone, but if you decide to join the overclockers club, make it an enjoyable journey. Visit the forums to read the reviews and advice. Learn from the good folks there that are always willing to help the newbie. Take your time, keep notes, and learn all you can. There's a lot of satisfaction in the knowledge and performance you can gain.